Textile designers are very creative. This is necessary because of seasonal factors and because the public taste continually changes, so the industry continually demands new products. Many designers in this industry would like the ability to custom-make their own yarns, so their products would be more unique, and so as to provide more flexibility in designing textiles.
Polyester (continuous) filament yarns have for many years had several desirable properties and have been available in large quantities at reasonable cost, but, hitherto, there has been an important limiting factor in the usefulness of most polyester flat yarns to textile designers, because only a limited range of yarns has been available from fiber producers, and the ability of any designer to custom-make his own particular polyester flat yarns has been severely limited in practice. The fiber producer has generally supplied only a rather limited range of polyester yarns because it would be more costly to make a more varied range, e.g. of deniers per filament (dpf), and to stock an inventory of such different yarns.
Also, conventional polyester filaments have combinations of properties that, for certain end-uses, could desirably be improved, as will be indicated hereinafter. It is important to recognize that what is important for any particular end-use is the combination of all the properties of the specific yarn (or fiber), sometimes in the yarn itself during processing, but also in the eventual fabric or garment of which it is a component. It is easy, for instance, to reduce shrinkage by a processing treatment, but this modification is generally accompanied by other changes, so it is the combination or balance of properties of any filament (or staple fiber) that is important. Generally, hereinafter, we refer to flat (i.e., untextured) filament yarns. It will be recognized that, where appropriate, the technology may apply also to polyester filaments in other forms, such as tows, which may then be converted into staple fiber, and used as such in accordance with the balance of properties that is desirable and may be achieved as taught hereinafter, but the advantage and need that the invention satisfies is more particularly in relation to flat filament yarns (i.e. untextured continuous filament yarns), as will be evident.
For textile purposes, a yarn must have certain properties, such as sufficiently high modulus and yield point, and sufficiently low shrinkage, which distinguish these yarns from feeder yarns that require further processing before they have the minimum properties for processing into textiles and subsequent use. These feeder yarns are sometimes referred to as feed yarns, which is how we refer to them herein, for the most part. Conventionally, flat polyester filament yarns used to be prepared by melt-spinning at low speeds (to make undrawn yarn that is sometimes referred to as LOY) and then drawing and heating to reduce shrinkage and to increase modulus and yield point.
It has long been known that such undrawn (LOY) polyester filaments draw by a necking operation, as disclosed by Marshall and Thompson in J. Applied Chem., 4, (April 1954), pp. 145-153. This means that the undrawn polyester filaments have a natural draw ratio. Drawing such polyester filaments has not been generally desirable (or practiced commercially) at draw ratios less than this natural draw ratio because the result has been partial-drawing (i.e., drawing that leaves a residual elongation of more than about 30% in the drawn yarns) that has produced irregular "thick-thin" filaments which have been considered inferior for most practical commercial purposes (unless a specialty yarn has been required, to give a novelty effect, or special effect). For filament yarns, the need for uniformity is particularly important, more so than for staple fiber. Fabrics from flat (i.e. untextured) yarns show even minor differences in uniformity from partial drawing of conventional undrawn polyester yarns as defects, especially when dyeing these fabrics. Thus, uniformity in flat filament yarns is extremely important. The effect of changing the draw ratio within the partial-draw-range of draw ratios (below the natural draw ratio) has previously had the effect of changing the proportions of lengths of drawn and undrawn filament in previous products. Thus, hitherto it has not been possible to obtain from the same LOY feed yarn two satisfactory different uniform yarns whose deniers per filament (dpfs) have varied from each other's by as much as 10%, because one of such yarns would have been non-uniform (or filaments would have broken to an unacceptable extent).
Undrawn polyester filaments have been unique in this respect because nylon filaments and polypropylene filaments have not had this defect. Thus, it has been possible to take several samples of a nylon undrawn yarn, all of which have the same denier per filament, and draw them, using different draw ratios, to obtain correspondingly different deniers in the drawn yarns, as desired, without some being irregular thick-thin yarns, like partially drawn polyester filaments. This is pertinent to a relatively new process referred to variously as "warp-drawing", "draw-warping" or "draw-beaming", as will be evident herein.
For many textile processes, such as weaving and warp knitting, it has been customary to provide textile yarns in the form of warp yarns carefully wound on a large cylinder referred to as a beam. A beaming operation has always involved careful registration and winding onto the beam of warp yarns provided from a large creel. Formerly, the warp yarns on the creel used to be drawn yarns, already suitable for use in textile processes, such as weaving and knitting.
Recently, there has been interest in using flat undrawn filament yarns, which have generally been cheaper than drawn yarns, and incorporating a drawing step in the beaming operation, as disclosed, e.g., by Seaborn, U.S. Pat. No. 4,407,767. This process is referred to herein as "draw-warping", but is sometimes called draw-beaming or warp-drawing. At least three commercial draw-warping machines have been offered commercially. Barmag/Liba have cooperated and built a unit, which is described and illustrated in Chemiefasern/Textilindustrie, February 1985, page 108 and pp. E14-15. There are also articles in Textile Month, March 1985, page 17, and in Textile World, May 1985, page 53. Karl Mayer/Dienes sell commercial draw-beaming systems, as advertised, e.g., on page 113 of the same February 1985 issue of Chemiefasern/Textilindustrie. The concept was discussed by Frank Hunter in Fiber World, September 1984, pages 61-68, in an article entitled "New Systems for Draw-Beaming POY Yarns", with reference to the Liba/Barmag and Karl Mayer systems using polyester POY and nylon. The Karl Mayer system was also described by F. Maag in Textile Month, May 1984, pages 48-50. Karl Mayer also have patents, e.g., DE 3,018,373 and 3,328,449. Cora/Val Lesina have also been selling draw-warping systems for some time, and have patents pending. These commercial machines are offered for use with polyester, polyamide or polypropylene yarns, the drawing systems varying slightly according to the individual yarns. As indicated, the object is to provide beams of drawn warp yarns, that are essentially similar to prior art beams of warp yarns, but from undrawn feed yarns. The advantages claimed for draw-warping are set out, e.g., in the article by Barmag/Liba, and have so far been summarized as better economics and better product quality.
As indicated, draw-warping had been suggested and used for polyester yarns. The article by Barmag/Liba indicates that POY, MOY or LOY yarn packages can be used to cut the raw material costs. POY stands for partially oriented yarn, meaning spin-oriented yarn spun at speeds of, e.g., 3-4 km/min for use as feeder yarns for draw-texturing. Huge quantities of such feeder yarns have been used for this purpose over the past decade, as suggested in Petrille, U.S. Pat. No. 3,771,307 and Piazza & Reese, U.S. Pat. No. 3,772,872. These draw-texturing feeder yarns (DTFY) had not been used, e.g., as textile yarns, because of their high shrinkage and low yield point, which is often measurable as a low T.sub.7 (tenacity at 7% elongation) or a low modulus (M). In other words, POY used as DTFY is not "hard yarn" that can be used as such in textile processes, but are feeder yarns that are drawn and heated to increase their yield point and reduce their shrinkage. MOY means medium oriented yarns, and are prepared by spinning at somewhat lower speeds than POY, e.g., 2-2.5 km/min, and are even less "hard", i.e., they are even less suitable for use as textile yarns without drawing. LOY means low oriented yarns, and are prepared at much lower spinning speeds of the order of 1 km/min or much less.
As has already been explained above and by Marshall and Thompson, conventional undrawn LOY polyester has a natural draw ratio. Attempts at "partial drawing" at lower draw ratios (such as leave a residual elongation of more than about 30% in the drawn yarns) will generally produce highly irregular "thick-thin" filaments, which are quite unsuitable for most practical commercial purposes. Among other important disadvantages, this severely limits the utility of LOY polyester as a practical draw-warping feed yarn. When undrawn polyester draw-texturing feed yarns of high shrinkage are prepared at higher spinning speeds, there is still generally a natural draw ratio at which these yarns prefer to be drawn, i.e., below which the resulting yarns are irregular; although the resulting irregularity becomes less noticeable, e.g., to the naked eye or by photography, as the spinning speed of the precursor feed yarns is increased, the along-end denier variations of the partial drawn yarns are nevertheless greater than are commercially desirable, especially as the resulting fabrics or yarns are generally dyed. Yarn uniformity is often referred to in terms of % Uster, or can be expressed as Denier Spread, as will be discussed hereinafter. It is not merely a question of denier uniformity, although this may be a convenient check on whether a yarn is uniform, as partially-drawn denier variations often mean the filaments have not been uniformly oriented along-end, and variations in orientation affect dye-uniformity. Dyeing uniformity is very sensitive to variations resulting from partial drawing. So, even for polyester POY prepared at relatively high spinning speeds, as will be seen hereinafter in the Example, partial drawing of such POY has produced yarn that is unacceptable, e.g., from a dyeing uniformity standpoint. Thus, hitherto, even with POY, such as has been used as feed yarn for draw-texturing (often referred to as DTFY herein), it has not been practical to draw-warp the same such POY (DTFY) to two different dpfs that vary from each other by as much as 10% and obtain two satisfactory uniform drawn yarns without significant broken filaments, because one would have been partially drawn.
Thus, it will be understood that a serious commercial practical defect of prior suggestions for draw-warping most prior undrawn polyester (POY, MOY or LOY) had been the lack of flexibility in that it had not been possible to obtain satisfactory uniform products using draw ratios below the natural draw ratio for the polyester feed yarn. This was different from the situation with nylon POY or polypropylene.
So far as is known, it had not previously been suggested that a draw-warping process be applied to a polyester textile yarn, i.e., one that was itself already a direct-use yarn, such as had shrinkage properties that made it suitable for direct use in textile processes such as weaving and knitting without first drawing. Indeed, to many skilled practitioners, it might have seemed a contradiction in terms to subject such a yarn to draw-warping because such a yarn was already a textile yarn, not a feed yarn that needed a drawing operation to impart properties useful in textile processes such as weaving or knitting.
According to the parent application (U.S. Ser. No. 07/338,251 referred to hereinabove, the disclosure of which is hereby incorporated herein by reference), processes were provided for improving the properties of feed yarns of undrawn polyester filaments. Such processes involved drawing with or without heat during the drawing and with or without post heat-treatment, and are most conveniently adapted for operation using a draw-warping machine, some such being sometimes referred to as draw-beaming or warp-drawing operations.
Preferred undrawn polyester feed yarns comprise spin-oriented polyester filaments of low shrinkage, such as have been disclosed in Knox U.S. Pat. No. 4,156,071. Alternatively, spin-oriented feed yarns of low shrinkage may be prepared at speeds higher than are used in the Knox patent, including speeds and conditions such as are disclosed by Frankfort & Knox in U.S. Pat. Nos. 4,134,882 and 4,195,051.
Recently, much interest has been shown in making sub-denier filaments, both for continuous filament yarns and for conversion into sub-denier staple. By sub-denier herein we mean, for convenience, any filaments having a denier (the weight in grams of a length of 9000 meters) per filament of about b 1 or less. The manufacture of sub-denier filaments commercially is more costly than for most prior commercial filaments of regular denier, as is well known. Much of the prior commercial filament yarns of regular denier have been made by spinning continuously at high withdrawal speeds. To make filaments of any required lower denier by a like continuous process requires correspondingly lower throughputs of polymer. Also, as the filament denier is reduced, it becomes progressively more difficult to maintain uniformity, both along-end and between the various filaments. Lack of uniformity often shows up in the eventual dyed fabrics as dyeing defects, so is undesirable.
The present invention provides a technique by which sub-denier polyester filaments may be made efficiently, without some of the cost disadvantages referred to above.